1. Field of the Invention
The present invention relates to medical devices and in particular, implantable medical devices.
2. Description of the Related Art
Medical devices related to managing, treating and providing therapy for cardiac conditions have changed and improved dramatically since their inception. Cardiac pacing, as an example, originally required an external pulse generator that itself required external power. While providing life sustaining therapy, patients were tethered to the power source and of course, power failures could prove catastrophic. Portable, battery powered external pulse generators were developed and provided the patient with the ability to be ambulatory; however, the pulse generator had to be carried by the patient. Furthermore, pacing leads were exposed through the patient's tissue and extreme care had to be exercised to minimize the risk of infection or inadvertent withdrawal.
Subsequently, fully implantable, battery powered pulse generators were provided in a hermetically sealed housing. This housing was rather large and was typically implanted in the abdomen of the patient, with leads extending to the heart. The size of such a device often made it rather uncomfortable and the implantation procedure was relatively invasive.
As technology improved, implantable medical devices (IMDs) have become continuously smaller, while offering increased longevity, reliability and many more features and therapies. Epicardial leads that were attached to an external wall of the heart were replaced with endocardial leads that are implanted transvenously, thus becoming minimally invasive. With these smaller devices, the housing was no longer placed in the abdomen but instead was implanted subcutaneously or sub-muscularly, often in the pectoral region. A “pocket” is formed underneath the skin or muscle sufficiently large to receive the housing of the IMD. The exposed or proximal ends of the leads are then connected to the housing and the incision is closed. While now routine, this is still a surgical procedure that requires skill and the appropriate medical facilities.
In general, patients are comfortable with these implanted devices and have a full range of motion, without interference or hindrance. Some patients feel the housing in the “pocket,” which may be physically and/or psychologically uncomfortable. Physically, some patients may press against the housing during certain physical activities making the housing noticeable. Even if not a hindrance or painful, simply “feeling” the presence of the device may remind that patient that they have a medical implant and/or medical condition and this alone may be troubling to that patient. Some patients develop a habit of pressing against the pocket and hence against the IMD and often rotating or twisting the IMD. Typically, IMDs that have one or more leads will have any excess lead length coiled under (or around) the housing of the IMD. Thus, frequent patient manipulation may cause portions of the lead(s) to twist or rub, potentially damaging the lead body or pulling the lead out of contact with the targeted tissue. This is sometimes referred to as “twiddlers syndrome.”
As the size and capability of IMDs has greatly improved, use of these devices has naturally expanded. This results in greater knowledge and acceptance among the patient population as well as within the medical community. As a result, caregivers are using IMDs with more frequency and for new and diverse purposes. For example, pacemakers are used in patients with various bradyarrhythmias. In such a patient, the heart's intrinsic pacing function fails or is deficient and the IMD provides electrical stimulation to maintain the proper heart rhythm. Such therapy is well known and is referred to above with the early, external pulse generators. Recently, the medical community has been using pacing technology in patient's whose heart rhythm is actually normal. Heart failure patients often have normal rhythm and conduction; however, this disease causes the heart to enlarge. As a result the left and right ventricles are unsynchronized when they contract even though the depolarization waveform triggering such a contraction was “timed” properly. Using cardiac resynchronization therapy (CRT), the left and right ventricles are paced, leading to a mechanical “resynchronization” of the left and right ventricular contractions. This not only leads to better immediate hemodynamic performance, but the heart itself often remodels itself (reducing in size) leading to an improvement in the disease state.
Not only are new therapies and treatments developing, implantable devices are now being used to collect sensor data for a variety of purposes. For example, implantable loop recorders (ILRs) are implanted subcutaneously and record cardiac data, unobtrusively, for extended periods of time. This allows robust medical data to be collected that, as a practical matter, may be otherwise unattainable.
These are merely two examples that illustrate the ever increasing trend to beneficially use implantable medical devices with greater frequency and for a wide variety of purposes that extend well beyond cardiac care. This presents a challenge to some caregivers who might want to use a given device for their patient but do not have the necessary surgical qualifications to actually implant the device. While such a patient may always be referred to another doctor, this adds cost and burden, some patients may not follow through, and some caregivers may simply opt for other treatments in order to maintain their relationship with the patient.